AGB stars are low mass stars at the end of their stellar evolution, in the process of losing a large amount of their mass in a massive stellar wind. They are thought to contribute a major fraction of the molecular content of the interstellar medium. However, the mass loss mechanism and evolutionary sequence is not very well understood. I will give a short introduction to the AGB group at the Stockholm Observatory and our reasearch with a short background on AGB stars in general. Our research includes modelling M-type, S-type and C-type AGB stars using dusty, monte carlo and accelerated lambda iteration codes. I might also mention something about detached shells around AGB stars.